Hydraulic brake, especially for lifting trucks



J. I OEF 2,075,857

HYDRAULIC BRAKE, ESPECIALLY FOR LIFTING TRUCKS April 6, 1937.

original Filed'sept. s, 1951 2 Sheets-Sheet l April C, -193.7. J, LOEF --2,o,7,5,s51'

HYDRAULIC BRAKE,V ESPECIALLY FOR LIFTING` TRUCKS O rfiginal Filed Sept. 3, 1931 2 Sheets-Shea*l 2 forny.

4@ www Patented Apr. 6, 1937 UNITED STATES v 2,075,851 HYDRAULIC BRAKE, ESPECIALLY Fon G TRUC Jakob Loef, Moosburg, Germany Application september 3, 1931, serai No. 551,033

Renewed April 4, 1935 s claims. (ci. iss-ss) The object of the present application is a, hydraulic brake, as is frequently employed, recently more especially in lifting trucks. In the application vof brakes of this kind it has been found that they do not give full satisfaction.

The hydraulic brakes -in lifting trucks are supposed to transform the potential energy of the lifted load into working power and heat when they are lowered. As is generally known, brakes of this kind consist of a cylinder andfa piston' '20 of the oil is proportional to the pressure produced in the oil-brake, and this pressure again depends upon the load resting on the liftingframe or the platform. This resultsin the disadvantage that big loads are lowered quickly and light loads considerably more slowly, giving rise in loads between 0 and 1500 kilos to differences of time which are 15 to 30 times as big.

It need hardly be emphasized that this fault is felt to disadvantage in practical work. VParticularly the lowering of the empty truck or the unloaded platform takes much too long, whereas in the case of-big loads the repressing effect of the brake is at times insuicient.

Several solutions have become known which are supposed to remedy this fault. It is particularly well known to build in a valve standing under the action of a spring which for quite light loads, i. e. for an empty truck plus the weight of a platform, holds open a larger redux-crosssectional area and which brings the contraction calculated for the maximum load into use only with a load which exceeds the one before-mentioned. But even this solution did not give satisfaction in practicalvwork, for it merely provided a, shortening of the lowering time for the unloaded truck, while light loads from about 100 to 15.0 kilos still required far too much-time.

-It has been attempted to remedy this fault by a device which has become known under the term of floweringregulator and which consists in an adjustment'by hand of the valve, so that 'a owing-through section of different size is given free for the refluxv ofv the oil.

The objection to this solution is that it does not work automatically and that it requires the control of a workman attending to it. On the other hand it also holds certain dangers as the oil-brake adjusted for moderate loads may, with heavier loads, cause a jerky lowering and thereby damage the load and the frames and endanger the workman. I

The constructions above described are considerably improved by the arrangement described in the following. Their faults are avoided and the advantage hitherto unknown is obtained that the oil-brake automatically adjusts itself to thel load and that the lowering-velocity can be maintained practically equal for all loads.

The object of the 'present application is illustrated by way of example in the accompanying drawings in which- Fig. 1 represents a longitudinal section through the oil-brake,

Fig. 2 the construction of a piston,

Fig. 3 the piston-pin,

Fig. 4 a top-view of the piston-pin of Fig. 3,

Figs. 5 and 6 different constructions of the pist0n,

pin,

Figs. l0 and 11 other constructions of the piston,

Fig. 12 the lifting truck with the brake view,

Fig. 13 the lifting truck of Fig. 12 in lateral view withV lowered platform and Fig. 14 with raised platform. 1

The oil-brake consists, in the manner known, of a brake-cylinder l, in which the piston 2 slides. This piston 2 is held true by means of piston-rings. The' brake-cylinder i is closed at its front end bythe cover 4 and at its rear end by the cover 5. The piston-rod 6, around which a screw-spring 1 is laid, passes through the rear cover 5, the screw-spring 'l acting on the piston 2 and supporting itself against the cover, 5. The piston-rod 6 is constructed hollow and contains in its inside another screw-spring 8 which presses with one end against the head 9 of the pin I0 which is passed through the piston. In the piston 2 there is a bore II which can be closed or opened by the pin I0. The oil c'an flow through this bore from the front to the back of the piston, thus effecting a locking of the piston. The pump is fastened Wth its front part l2 to the in top driving-frame and with the eye I3 of the pistonrod 6 to the lifting-frame. The piston 2 is thereby pulled into the rear position and the major part of the oil is in front of the piston. The pis- Figs. '7, 8 and 9 different constructions of the l 45 cylinder I ton-rod 6 is built in the form of. a tube in its front part I4 the latter being providedf with openings I5 from which the oil can emerge from the piston. With the exception of a valve conpressure. Therefore-and that is the guiding thought of the present applicationthe crosssectional area of the pin I0 is so calculated that a spring 8 resting on this pin can be constructed strong enough to guide the pin against the pressure and be housed in the piston-rod I4 which for this purpose is made hollow. For constructive reasons the piston-rod is not hollowed out in its entire length but is divided in a hollow part I4 and a solid part 5. The hollow part still possesses a. slight enlargement I'S in which a piston 9 fastened to the pin-valve I0 slides. This enlargement serves to sto`p the stroke for the valve I0. The piston itself possesses a bore II which is carriedthrough to about its middle and which endsfin a circumferential groove I1 cut into the bore in which the pin valve III slides, as shown in Fig. 2. The bore II can also be carried out obliquely (Fig. 2). It is also possible to connect the groove I1 to a bore I1a terminating in a bore I8 as shown in Fig. 5 so that the brake-huid need not take its waythrough the central bore of the piston and does not enter the inside of the piston-rod but leaves the piston through the bore I8. In order to effect the entry of the fluid from the central bore into the inside of the pistonrod I4, the piston 9 of the valve I0 has been provided with a bore as shown in Figs. 3 and 4, while the piston-rod I4 possesses bores I5 through which the oil can emerge from the piston rod into the The valve I0 can slide in longitudinal direction in the bore IB of the piston-rod, and corresponding to this longitudinal mobility the pin may be of various constructions which serve to contract the cross-section. These constructions may consist of a conically tapering groove I9 of the pin as shown in Fig. 3. They may consist also of a conical turning 20 (Fig. 5) or of an arrangement of furrows 21| (Fig. '1) or a number of holes with increasing diameter 22 (Fig. 8) or nally of holes with invariable diameter but with increasing density, 23 (Fig. 9). The essential point is that the cross-section narrows under the pressure of the enclosed fluid, by the pin III being pushed into the piston through the pressure lying on its head-end, against the action of the spring 8. Alternatively as illustrated in Fig. 6 it is possible to perforate the pin at Illa, which would offer constructive advantages in so far as its diameter becomes enlarged, since the ringsurface gives the same cross-section as the face of the solid pin only with enlarged diameter. In this case the means to contract the cross-sectional area are arranged inside the piston and the bores do not serve for the admission but for the exhaust of the brake-fluid.

The manner of action of the oil-brake is as follows:

When the lifting-truckis raised the piston is drawn from the cylinder, the spring 1 which is fitted onthe outside of the piston-rod 6, I4 being compressed.A The brake-fluid takes its way through the holes I5, the hollotw interior -of the piston-rod I4, the bore I9 of he valve I0, the bevelment of the pin III, the channel II and collects behind the piston. During this process the valve is in the position on the far left, as shown in the drawings, and the .widest cross-section of the pin is opposite the groove I1.

When the lowering movement is started the load presses on the piston by meansof the pistonrod and thereby on the fluid compressed in the cylinder in front of the piston. Proportionately to this pressure the pin of the valve is pushed backward in the piston 2, the cross-sectional area becoming narrower and the reflux-velocity of the brake-duid correspondingly slower.

As indicated in Figure 10 of the drawings, the piston rod may be made rigid with the piston and in this particular construction the valve pin I0 extends in an offset position through the piston 2 and is connected to a spring actuated lever 25.

As will appear from Fig. 11, instead of one pin several may be used working either separately or jointly by means of a disk 25 uniting the pins and acted upon by a spring 21.

Figs. 12, 13 and 14 show a lifting-truck of this kind with the brake. The lifting-truck consists of the driving-frame or carrying-frame or carrying-frame proper 24, in which fixed wheels 25 are supported at the rear end, whereas the guiding wheels 28 which can be swung round are provided at the cross-piece 21 on the forward part. Above the carrying-frame is the lifting-frame 23 which can be swung on the axle 3I of the hind wheels by means of guide-rods 30 and around the forward pivot 32 by means of guide-rods not shown. and is thereby lifted to a maximum height. This lifting movement is effected by means of the radius-bar 33 which engages a lifting-jaw 35 on the lifting-frame by -means of a head 34. A transom-bar 36 is provided at the carrying frame 24 to which the rear end of the brake I is fastened. The piston 6 which can be pulled out of the brake is fastened with its front part I3 to the transom-bar 31 which again is arranged at the upper frame 29. When the lifting-truck is raised through the radius-bar 33 catching behind the jaw 35 with its head 34, the brake is pulled out, the spring 1 being compressed. Now, in lowering,the upper frame will only gradually be able to go down according to the flow of oil through the piston. The velocity-of lowering respectively of the oil-passage depends proportionally on the load, so that with heavy loads the frame drops slowly and with light loads the upper frame drops quickly.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed I declare that what I claim is:

1. In a lifting truck having a carrying frame and a lifting frame movable upon said carrying frame, a hydraulic brake for checking the lowering movement of the lifting frame, comprising a fluid cylinder having one end connected to one of said frames, a piston rod received in said cylinder through the free end thereof and connested at its outer end portion to the other of said frames, a piston carried by the piston rod and reciprocating with the latter in the cylinder,

a passageway formed in said piston and establishing communication between the cylinder spaces in front and in back of the piston, a valve slidably mounted in said piston and interposed in the passageway, means on said valve to vary amasar the cross sectional area of said passageway with the sliding movement of the valve, spring means acting upon the valve and normally urging the latter to a position corresponding to the maximum effective cross sectional area of said passageway, and other spring means encompassing said first-named spring means and acting upon the piston.

2. In a lifting truck having a carrying frame and a lifting frame movable upon said carrying cation between the cylinder spaces infront and" in back of the piston. a pin valve slidably mounted in said piston and interposed in the passageway, means on said pin valve to vary the cross sectional area of said passageway with the sliding movement of the valve, a head rigid with said valve and positioned within the hollowed section of the piston rod. a coil spring disposed within the hollowed section of the piston rod and bearing uponthe head of the valve, and another coil spring about the piston rod and act- A ing upon the piston.

3. In a lifting truck having a carrying frame and a lifting frame movable upon said carryingframe, a hydraulic brake for checking the lowering movement oi' the lifting frame. com'- prising a fluid cylinder having one end connected to the carrying frame, a piston rod received in 40 said cylinder through the free end thereof and connected at its other end to the lifting frame.

the inner end portion of said'piston 'rod having a hollowed section, a piston carried by said section. of the piston 4 rod and reciprocating with the latter in the cylinder, a passageway formed in said piston and establishing communication between the cylinder spaces in front and in back of the piston, a pin valve slidably mounted in said piston and interposed in the passageway,

said pin valve having a portion extending into the hollowed section of the piston rod, means on said pin valve to vary the cross sectional area ofl said passageway with the sliding movement of the valve, spring means disposed within the holu lowed section of the piston -rod and acting upon the extended portion of the pin valve, and other spring means acting upon Athe piston. t

4. A hydraulic brake of the type used for checking the lowering movement of a lifting:y truck t ,platform and comprising a cylinder, a piston fitted for sliding movement in said cylinder, with the movement oi said piston in said cylinder resisted by a iluid, said piston having a bore, a

valve mounted in said bore, said valve being movable in said bore in response to the pressure generated through movement of theu piston against the fluid in said cylinder, a spring for resisting said pressure induced movement of the valve, said piston having a passage leading from the pressure side of said piston to said valve bore,

-said valve -'being normally. maintained by its spring in a position inwhich it permits substantially free ilow of liquid through said passage and saidvalve bore to the other si of the piston, and means whereby the iluid pressure may be directed against the said valve independently of said passage to urge said valve into positions corresponding to varying restriction of the ow of liquid through said passage.

5. A hydraulic brake of the type used for checking the lowering movement of a lifting truck platform and comprising a cylinder, a piston iitted for sliding movement in said cylinder. with the movementof said piston in said cylinder resisted by a fluid, said piston having a bore axially formed therein parallel to the direction of movement of said piston and in communication with the pressure end of said piston, a valve mounted in said bore for movement parallelto the movement of said piston and exposed to the pressure generated at the pressure end of said piston, said valve being movable in said bore relatively to said piston in response to the pressuregenerated through movement of the piston against the fluid in the cylinder and in a direction reverse to the direction of movement of said piston, a spring for resisting the said pressure induced movement of the valve relatively to the piston, said piston having a passage leading from the pressure side of said piston to said valve bore and then to the other side ot said pistn, said valve being normally maintained by its spring in a position in which it permits substantially free ow of liquid through said passage to the other side of the piston, the movement of said valve relatively to said piston being effective to restrain the flow of liquid through said passage. A

6. A hydraulic brake for checking the lowering movement of a li'fting truck comprising a cylinder. a piston tted for sliding movement in said cylinder, said piston having. a' valve .bore terminating on the pressure side of the piston, a graduated valve in said bore and having a portion` thereof disposed in said bore so as to be actuated by the pressure on the pressure side of the piston. said piston havinga i'urther passage leading to said valve bore from the pressure side of said piston, a spring adapted to urge said valve into r a position in which it permits substantially free -ilow of liquid through said passage' and said valve, the pressure .in said piston valve borel against the said v alve portion being eifective to move said valve against the spring pressure and into a position substantiallyv restricting the ow of liquid through said passage.

` JAKOB LOEF. 

